PDF and Hardcover, 80 pages
The Core Rules weighs in at 80 pages and gets to the very heart of the OSE line. The essential Essentials as it were. It covers Ability scores in general, sequences of play and all the basic rules needed. Combat is covered separately. Magic also gets a bit of coverage here in general terms and including how spells can be researched and magic items made.
The rules have been "cleaned up" from their obvious predecessors. The focus is on readability and playability here. like all of the OSE books every entry of a rule is presented on facing pages. So you open up the book and everything you need on the subject is right there. Only rarely will you need to turn the page.
In the original rules, it took a bit of digging to actually figure out how much a character moves. This was vastly improved in later editions of the game, but here it is very succinctly spelled out. Other rules are equally made clear.
Since the "Basic" and "Expert" rules are combined here there is an economy of word usage here. As much as I love my Basic and Expert games, sometimes you need to consult both books when a situation comes up. This book though is more than a handy index, it takes that notion from the B/XE Core Rules and expands it into a much more playable game.
The philosophy of the Core Rules is just that, everything you need to play regardless of the genre. Included in the boxed set (and an expected purchase) is the Classic Fantasy Genre Rules. This is what takes the Core Rules and makes it into a "Basic-era Fantasy Game". So in simpler language, this is Basic D&D. You do need a set of Genre Rules to be able to use the Core Rules, but there is enough there if you are an aspiring game designer to make up your own. Say Roaring 20s, or Space or Horror. Anything really.
The book has some really, really great old-school feeling art as well. Just fantastic stuff really.